A mechanical seal, an example of a slide component, is evaluated for its performance by a leakage rate, a wear rate, and torque. In conventional arts, by optimizing the seal material and the sealing face roughness of mechanical seals, their performance is improved to achieve low leakage, long life, and low torque. However, due to growing awareness of environmental problems in recent years, a further improvement in the performance of mechanical seals has been demanded, for which technology development beyond the limits of the conventional arts has been required.
To respond to this, the present applicant and others have developed mechanical seals with surface texture such as Rayleigh steps, reverse Rayleigh steps, reverse spiral grooves, or U-shaped or nano-level projections and depressions used on a sealing face in order to achieve a tradeoff between torque reduction and leakage rate reduction in slide components such as mechanical seals (see Patent Documents 1, 2, and 3, for example).
It has heretofore been confirmed that in a mechanical seal of a water pump used for cooling a water-cooled engine, for example, an additive in LLC, a type of antifreeze, such as silicate or phosphate (hereinafter, referred to as a “deposit formation-causing substance”) can be concentrated on a sealing face, forming deposits as time passes, and degrading the function of the mechanical seal. The deposit formation is considered to be a phenomenon that occurs likewise in mechanical seals of apparatuses that handle chemicals or oils.
The present inventors' study has confirmed in experiments that in a mechanical seal in which surface texture is used, negative pressure can be generated in a sealing face due to its characteristics, and a sealed fluid entering the sealing face evaporates due to the negative pressure, causing excessive precipitation and formation of a deposit formation-causing substance, and formation of deposits at an accelerated rate, so that the function of the mechanical seal may be degraded. Further, a concentrated and evaporated fluid leaking to the outside of the sealing face can be brought back by negative pressure, thereby being deposited on the sealing face.
For the prevention of deposit formation on a sealing face, the present applicant has filed a patent application earlier for an invention that reduces negative pressure at low pressure fluid-side ends of pumping grooves (portions upstream of a fluid flow associated with a relative movement to an opposing sealing face) communicating with the high-pressure fluid side for forcing a sealed fluid back to the high-pressure fluid side to prevent the occurrence of evaporative cavitation, and thereby to prevent formation of precipitates at the low pressure fluid-side ends of the pumping grooves (see Patent Document 4).
The applicant has also filed a patent application for an invention in which, in a slide component with fluid discharge means for discharging a fluid to the high-pressure fluid side, a buffer groove for reducing the entry of a low-pressure fluid into the high-pressure fluid side is provided in a sealing face on the low-pressure side of the fluid discharge means, and the buffer groove constitutes a buffer for the low-pressure fluid entering the sealing face from the low-pressure fluid side against a high-pressure fluid, to delay the time before the sealing face is filled with the low-pressure fluid (e.g., air), and to prevent the dehydration and condensation reaction of the high-pressure fluid (see Patent Document 5).